1. Field of the Invention
The present invention relates generally to the art of rechargeable batteries and more particularly to the thermal management of battery cells.
2. Description of the Prior Art
Small rechargeable batteries are becoming increasingly important with the continuing development of portable electronic appliances, such as uninterruptible power systems (UPS). The batteries which are used with such devices are frequently referred to as flat pack batteries. It is highly desirable that such batteries be compact and light in weight yet have a high storage capacity.
Advances have been made in this technology in recent years, even using conventional lead-acid battery technology. Lead-acid batteries typically suffer from weight disadvantages due to the weight of the plate materials (lead plates and lead-containing active materials) and the weight of the containers which are required to hold the plates and electrolyte. Lead-acid batteries, however, have very good power delivery characteristics and may be repeatedly recharged and even overcharged, with only minimal damage to the cells. Moreover, the power curve of lead-acid batteries is relatively predictable. Such features are not readily achievable with other batteries, such as nickel cadmium batteries.
One type of lead-acid battery is the recombinant battery which differs from conventional lead-acid batteries (for example, automobile batteries) in that there is no flowing electrolyte in the system. Substantially all of the electrolyte is maintained in separator material, typically made of a glass fiber mat, located between the plates. The gasses evolved during the electrochemical reactions which take place in lead-acid batteries are absorbed and recombined within the battery rather than being vented in the normal case. With such systems, the battery can be sealed and made maintenance free. Other recombinant systems still use valves to relieve any undesirable build-up of pressure within the cells of the battery.
One recent development in the field of recombinant lead-acid batteries is described in U.S. Pat. No. 4,996,128 issued Dec. 26, 1991 to Aldecoa and Miller entitled "Rechargeable Battery" (hereafter, the "'128 patent"). The battery described in this patent includes a thin plastic casing having generally rectangular top and bottom portions, the casing including lead foil sheets for the positive and negative plates, each foil being pasted with an appropriate active material. Separator layers are placed between the active material. Another embodiment is described, wherein a single positive plate is located at the center of the casing, while two negative plates are disposed on either side, the latter being separated from the positive plate by layers of separator material. Further embodiments are described, including multi-layer batteries of the bipolar variety.
Common features of the batteries described in this patent are the support members which extend through the plates. The support members in the illustrated embodiments are plastic pins which may extend from one or the other of the casing portions, which pass through the plates and are attached to the opposite casing portion (for example, by vibration welding). Alternatively, pin segments from each casing component may pass partially through the cell and are joined at their tips by an appropriate process such as vibration welding. The support members are provided in a pattern which insures even support and which permits even compression of the battery components when the periphery of the casing portions are sealed. Other recombinant lead-acid batteries are described in the background section of the aforementioned '128 patent. That patent is specifically incorporated herein by this reference.
While the battery systems described in the '128 patent provide numerous advantages over prior art systems, one drawback exists in connection with the thermal management of those batteries. The problem is particularly pronounced when a plurality of individual cells are stacked, one on top of the other, and there is no effective way of dissipating heat, particularly from the intermediate cells. A battery system which would overcome that drawback would represent a significant advance in this technology.